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Introduction from initial water-soaked lesions (Coerper, 1919). Psg is a cold-weather pathogen, i.e. the disease occurs only after periods of cold and humid weather, and virulence determinates of Psg are regulated in a temperature-dependent manner (Smirnova & Ullrich, 2004; Weingart et al., 2004). The best studied virulence factor of Psg is the phytotoxin coronatine, responsible for chlorosis formation in infected tissue. Coronatine is a structural analogue of the plant signaling compound, methyl jasmonate. In host plant tissue, it is able to induce a systemic resistance response that is targeted against insects. By this meddling with plant signal pathways, Psg misleads defense response of the host and suppresses the SAR-pathway that would correctly address the bacterial pathogen (Bender et al., 1999; Cui et al., 2005). The antagonist Pss22d belongs to the same species, but to a different pathovar. It has been isolated as possible biocontrol agent in a screening for soybean phyllosphere epiphytes (May et al., 1997a). During that study, 82 epiphytes isolated from healthy soybean plants were tested for their ability to suppress different strains of Psg in agar diffusion assay (in vitro) and in a laboratory in planta assay (Tab. 2). Due to its excellent performance Pss22d was selected for further studies. Tab. 2. Screening of soybean phyllosphere for antagonists against Psg. Correlation between in vitro and in planta inhibition of Psg by 82 tested soybean epiphytes. Source of data: May et al., 1997a Isolates Number of strains with inhibitory activity Number of tested strains in vitro in planta in vitro and in planta Pseudomonas spp. 11 6 4 3 Pantoea agglomerans (formerly Erwinia herbicola ) 27 13 9 4 Enterobacter/Erwinia 11 5 2 2 Xanthomonas spp. 8 2 1 0 other Gram-negative bacteria 11 1 2 0 Gram-positive bacteria 14 2 1 0 15
Introduction Pss22d demonstrated a high epiphytic fitness. After artificial wound inoculation of greenhouse-grown soybean plants it established a stable population that stayed constant for several weeks whereas other saprophytes could not be reisolated after more than three days post inoculation (May et al., 1997a; May et al., 1997b). In the follow-up field trials Pss22d showed a satisfactory epiphytic fitness. It formed a population of about 10 6 colony forming units (cfu) per gram fresh weight of plant material after spray inoculation. This population size was stable over the entire vegetation period and made up 10-40 % of the total epiphytic population. Simultaneous application of Pss22d and Psg1a lead to a significant suppression of the pathogen. The population density of Psg was reduced by as much as two orders of magnitude. When the antagonist was inoculated four weeks prior to pathogen application, this inhibitory effect was even enhanced. At the end of the growing season the pathogen population reached only 1/800 (ca. 10 4 cfu/g fresh weight) of the population size it reaches in absence of the antagonist, i.e. ca. 10 7 cfu/g fresh weight (Völksch & May, 2001b). As mentioned above, the molecular basis of this interesting control system is undetermined until now. Nevertheless, there are the following hypotheses. Pss22d belongs to the group of fluorescent pseudomonads. Although the active principles determined for this group so far have been studied mostly in the rhizosphere, they comprise a starting point for the assessment of similar mechanisms in the phyllosphere. Consequently, antibiosis and siderophores production come into focus of two separate studies. Toxin production by Pss22d has already been demonstrated in vitro, yet it is necessary to investigate the importance of antibiosis in planta (Völksch et al., 1996). This is currently investigated by Sascha D. Braun at the University of Jena. The general importance of siderophore production for biological control by fluorescent pseudomonads gave rise to a first assessment of siderophore production by Pss22d and Psg. CAS-agar is a general indicator medium for the 16
Page 1 and 2: Siderophore production of Pseudomon
Page 3 and 4: Acknowledgements This project was s
Page 5 and 6: Abbreviations Ach achromobactin-lik
Page 7 and 8: Contents 4.1.2 Pseudomonas syringae
Page 9 and 10: Contents 5.3 Influence of sideropho
Page 11 and 12: Introduction 2 Introduction Like hu
Page 13 and 14: Introduction In contrast to the rhi
Page 15 and 16: Introduction 2.1.2 Host, pathogen a
Page 17 and 18: Introduction The relationship betwe
Page 19 and 20: Introduction developement of resist
Page 21 and 22: Introduction Fe 2+ + H 2 O 2 → Fe
Page 23: Introduction 1997a; May et al., 199
Page 27 and 28: Introduction 2.4 Aim of this study
Page 29 and 30: Material and Methods Tab. 4. Antibi
Page 31 and 32: Material and Methods Iron-free 5b m
Page 33 and 34: Material and Methods Solution3, car
Page 35 and 36: Material and Methods 3.6 Plasmids T
Page 37 and 38: Material and Methods PCR-Screening
Page 39 and 40: Material and Methods on ice for 10
Page 41 and 42: Material and Methods stained in eth
Page 43 and 44: Material and Methods 4.2.5.3 Conver
Page 45 and 46: Material and Methods 4.2.5.9 Ligati
Page 47 and 48: Material and Methods strains were s
Page 49 and 50: Material and Methods 9.5). For sign
Page 51 and 52: Material and Methods gentle shaking
Page 53 and 54: Material and Methods columns were w
Page 55 and 56: Results 5 Results 5.1 Analysis of s
Page 57 and 58: Results The 13-kb open reading fram
Page 59 and 60: Results If integration is due to a
Page 61 and 62: Results Yersiniabactin is a siderop
Page 63 and 64: Results Next, a large number of tra
Page 65 and 66: Results Nevertheless the site of tr
Page 67 and 68: Results Achr2_KpnI_rev binding site
Page 69 and 70: Results Interestingly the mutant Ps
Page 71 and 72: Results XAD4-purification yielded i
Page 73 and 74: Results After changing the mobile p
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Results P P A Fig. 21. Isoelectic f
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Results reduced in comparison to th
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Results A-E represents single inocu
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Results Tab. 10. Development of pop
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Results Tab. 11. Distribution of th
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Discussion bacteria with redundande
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Discussion 6.2 Possible regulation
Page 89 and 90:
Discussion stationary phase transit
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Discussion and bacterium (Loper et
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Literature Bultreys, A., Gheysen, I
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Literature Galperin, M. Y. (2006).
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Literature Mazzola, M. (2002). Mech
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Literature Schubert, S., Rakin, A.,
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Literature Zou, J., Rodriguez-Zas,
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